The general field of holographic lenses has been in existence for a number of years. A hologram is a recording of the interference between two coherent beams of light. These beams are referred to as the reference beam and the subject beam. When this recording is reilluminated by the reference beam, the hologram reconstructs the subject beam as though the subject was still present. This means that if the subject was a solid object like a coffee cup, the viewer can look through the hologram (much like looking through a window) and see the coffee cup in three dimensions, without the coffee cup actually being present.
When the subject beam is not reflected from some part, but rather is a spherically expanding or contracting light beam, then the hologram will act as a lens, redirecting the reference beam light from its path to that originally taken by the subject beam in the holographic recording. The predominate use of such holographic optical elements (herein referred to as HOEs) has been to direct the scan of a laser beam (for use in bar code scanning), and to redirect the image of a heads-up display (used, for example, in military aircraft). In each of these cases, the HOE is being used to replace a more complicated linear set of lenses for the benefit of using only one element, and as in the case of bar code scanners, greatly reducing the cost of a system to form a complicated scan pattern.
In recent years, researchers such as H. Kogelnik of Bell Systems and J. Goodman of Stanford University have shown that special holographic optical elements can be used to provide a high degree of correction for use with diode lasers helping to create a better focus. In this work, it is pointed out that HOEs typically suffer from high chromatic aberration, making them impractical for several general applications. Multi-element HOEs, as well as HOEs in use with refractive lenses have shown to be useful over a limited wavelength range.
Other applications of HOEs has included: Fourier transform lenses, holographic encoders, laser range finders, solar concentrators, telocentric optics, fiber optic couplers, infrared lenses, and optical processors. Each of these systems work as a linear lens system collecting light from a well behaved, directional light source, typically laser, and redirecting the light.
Accordingly, it is an object of this invention to utilize in combination a non-point or extended and diffuse light source and a holographic optical element (HOE) for purposes of redirecting the light from the source along an axis to infinity and a specific viewing pattern positioned along the axis of the redirected light.
It is a further object of the invention to provide the combination, as aforesaid, in a traffic light.
It is a further object of the invention to provide the combination, as aforesaid, to create a task light without the requirement of a spaced reflector oriented on a side of the light source remote from the HOE.
It is a further object of the invention to provide the combination, as aforesaid, in an overhead room and/or area lighting fixture.
It is a further object of the invention to provide the combination, as aforesaid, in a vehicular interior and/or exterior light.